This is a study of pulmonary mucociliary transport in the two major chronic lung diseases of children: cystic fibrosis (CF) and asthma. Major objectives: 1) To characterize mucociliary transport in patients with CF and asthma and to relate this function to the type and extent of lung disease. Initial studies have shown that mucus transport is markedly impaired in CF; asthmatic patients have not been studied. 2) To explore pharmacologic methods for stimulating mucociliary transport and their effectiveness as therapeutic agents. Preliminary studies indicate that the administration of terbutaline results in a statistically significant increase in tracheal mucus velocity in patients with CF. The effects of terbutaline sulfate and other drugs will be studied in hopes of documenting improvement of mucociliary function. 3) To study the effect of aerosols and mucolytic agents on mucociliary transport in CF. Aerosols and mucolytic agents are routinely used in treatment of obstructive lung disease, but there is little objective evidence of their efficacy. This study will evaluate these agents by a direct, objective, and quantitative method. Mucociliary transport function will be studied by measuring the rate of transport of Teflon markers across the tracheal mucosa. The markers are placed on the mucosa through a fiberoptic bronchoscope and their motion filmed. The rate of motion is determined from the change in image size of each marker with time. The average velocity of a number of markers is expressed as "tracheal mucus velocity". The usefulness of this method has been documented by one group of investigators and is currently the only direct way to observe and quantitate mucociliary transport in humans. This method is particularly suited for study of drug effects, since measurements are completed over a period of only 2-5 minutes.